US3818733A - Piercing process - Google Patents

Abstract

An improvement in the piercing of difficult to pierce metal alloy billets where the billet is drilled throughout its axial length, a lubricating material such as glass inserted in the fore end of the bore of the billet, and the billet then heated to a working temperature. The hot billet is readily pierced with the lubricant facilitating in the piercing process.

Description

United States Patent [191 Ca'uley et al.

[ June 25, 1974 PIERCING PROCESS [75] Inventors: William J. Cauley, Beaver Falls;

Joseph F. Maykuth, Aliquippa, both of Pa.

[73] Assignee: The Babcock & Wilcox Company, New York, NY.

[22] Filed: July 17, 1972 [21] Appl. No.: 272,614

[52] US. Cl. 72/41, 72/209 [51] Int. Cl B21b 17/10 [58] Field of Search 72/41, 42, 46, 209

[56] References Cited I UNlTED STATES PATENTS 1 2,630,220 3/1953 Sejournet 72/42 2,791,924 5/1957 Sawyer .Q. 72/42 2,956,337 10/1960 Buffet et al. 72/41 3,335,589 8/1967 Buffet 72/4l FOREIGN PATENTS OR APPLICATIONS 2,007,250 9/1970 Germany 72/42 Primary Examiner-Charles W. Lanham Assistant Examiner-E. M. Combs [5 7] ABSTRACT An improvement in the piercing of difficult to pierce metal alloy billets where the billet is drilled throughout its axial length, a lubricating material such as glass inserted in the fore end of the bore of the billet, and the billet then heated to a working temperature. The hot billet is readily pierced with the lubricant facilitating in the piercing process.

4 Claims, 6 Drawing Figures 1 PIERCING PROCESS The present invention relates to improvements in rotary piercing processes and the like and more particularly to the rotary piercing of hot billets of stainless steel alloys and other metals and metal alloys difficult to pierce, in the manufacture of seamless hollows or tubes.

All commercial rotary piercing processes have the common feature of the formation of a hollow by peripherally rolling a hot cylindrical billet over a conical mandrel by driven rolls set at an angle to the horizontal plane through the center line of the piercing mill. The action' of the piercer rolls or cones consists of gripping the hot billet, advancing it by reason of the skew rolling action imparted by the feed angle of the roll axes, reducing the diameter of the billet, and then helically rolling the reduced billet over the conical mandrel between the driven rolls and offset guide rolls.

The rotary piercing of high alloy steels of the stainless type, even when the alloy constituents have been balanced in an effort to stabilize the phase of the alloy and effect improvement in high temperature ductility, has proved to be much more difficult than piercing billets of carbon steels. A suitable metal ductility when hot is necessary to withstand the various tensional, compressional, and torsional forces set up in piercing. The deformation of the metal in rotary piercing involves peripheral skew rolling which is largely compressive in nature, a reduction in wall thickness, a bending action on the outermost and innermost surfaces of the hollow, an abrading action on the inner and outer surfaces of the hollow caused by differences in the relative surface speeds of the hollow, mandrel and the driven and guide rolls, and a twisting action caused by the differential peripheral speeds of the hollow and the rolls at various points in the pass. A high degree of care must be exercised in such cases to provide the proper roll feed angle, suitable speeds of the piercer rolls, and a careful location of the piercing point to minimize internal marking of the pierced hollow. To secure the proper relative positions of the piercing point and billet, it is now customary to provide by drilling, burning or punching a center recess or starting hole in the billet end in which the piercing point is centered at the start of the piercing operation.

Even when the piercing point is made of a metal or metal alloy which has the desired qualities of toughness and wear resistance at high temperatures, and which does not spall or crack at the surface when the working layer is heated to a high temperature while the body remains at a much lower temperature, it has been found with billets of the character described, that the internal surface of the pierced hollow has been marked or fissured to an extent requiring a further conditioning operation to secure the desired inside finish before repiercing or drawing the pierced hollow. Efforts have heretofore been made to lubricate the piercing point to lengthen the working life of the point, and also to improve the internal surface condition of the hollow.

An effective means for lubricating the piercing operation was disclosed in the Sawyer US. Pat. No. 2,791,924 wherein ordinary bottle glass in solid or fiber form was inserted in the facing end of a hot billet immediately prior to the hot piercing of the billet. This process however has certain practical drawbacks both from a mechanical and process standpoint. Due to manipulative problems in handling a hot billet, it has been found difficult to properly insert the lubricating material in the end of the hot billet and to maintain the material in position during the piercing operation. Sometimes the lubricating material will be exuded outwardly of the billet during initial piercing point operation leaving insufficient material for effective lubrication of the outward end of the billet. This is particularly true when piercing longer billets which is the modern procedure, where billets are twice as long as those handled 15 to 20 years ago.

In the present invention we have overcome the above difficulties of providing adequate and reliable lubrication during the piercing process. This is accomplished by drilling the billet throughout its length and inserting the lubricating material in the billet prior to heating the billet to its working temperature. The lubricating material may be in any suitable form, however we have found it convenient to use rods or bars of sintered window glass and to fix the rods in the fore end of the bore by fiber glass. Since in the usual course of events the billets will be subjected to acertain amount of handling by cranes and the like the lubricating material must be securely placed in the bore of the billet to withstand such handling particularly before the billet is heated. Heating the billet to a working temperature will increase the integrity of the lubricant material in the bore due to a limited melting of the glass and adhesion to the metal of the billet. Of the drawings:

FIG. 1 is a diagrammatic illustration of a cone-type piercing mill, to which the operation of the invention is applicable;

FIG. 2 is a vertical section through the fore end portion of a billet with the lubricating material in position;

FIG. 3 is an end view of the billet shown in FIG. 2;

FIG. 4 is a section view of a billet with lubricating material positioned therein;

FIG. 5 is a section of a billet taken on line 5+5 of FIG. 4; and

FIG.'6 is a perspective view of a glass rod prior to insertion in the billet.

While the present invention is also adapted for use in other commercial types of piercing mills, such as the Mannesmann or parallel axis barrel type roll piercing mill or the Stiefel or 180 disc mill, it has been illustrated as applied to a 60 cone roll piercing mill in which a solid billet 10 is rotated and advanced by a pair of angularly arranged diametrically opposite rolls l2 rotated in the directions indicated by the arrows in FIG. 1 to cause the rotating billet to flow over and about a conical piercing point 14 mounted on a bar 16. The piercing point is held against longitudinal movement but is free to rotate with the billet being pierced.

In the invention procedure the workpiece or billet 10 will usually be cylindrical, and a typical size will be 5 to 8 inches in diameter and to inches long. The billet will be center drilled along the longitudinal axis to a bore 18 diameter of about 1 inch. The billet will then be counterbored on one end to form a conical opening 20 of about 2% inch base merging into the 1 inch bore. Extending the bore throughout the length of the billet will aid in maintaining reasonable concentricity of the pierced workpiece with a reasonable uniformity of pierced billet wall thickness.

After the billet has been bored, the lubricant will be inserted in the bore 18 adjacent the conical end 20. The lubricant advantageously will be a glass, such as window glass, which may be powdered, solid or fibrous. We have found that sintered glass particles formed as 10 inch long half round rods 22 with a A inch diameter are convenient for the purpose, see FIG. 6. The rods of semi-circular cross-section are inserted in the bore 18 in end adjoining pairs and packed in glass fiber 24 to retain their positioned relationship in the bore of the billet. Thus in all sizes mentioned, the 20 inches of glass material, positioned adjacent the enlarged or conical end 20 of the billet 10 will provide sufficient lubrication for billet piercing without appreciably exceeding lubrication requirements. lt will be understood that excessive amounts of lubricant can lead to piercing difficulties where glass may deposit on the rollers 12 causing slippage and incomplete piercing operations.

With the lubricant positioned as described, the billet 10 will be positioned in the furnace for heating to proper working temperatures. In the usual billet heating furnace the billets are maintained in a horizontal position throughout the heating cycle and the softening of the glass lubricant such as the rods 22 and fiber 24 will tend to increase the positional stability of the glass in the bore 18. As the billets, at the desired temperature are moved from the furnace to the piercing rolls, the billet will normally be maintained in a generally horizontal position so that the glass lubricant will be retained at its proper location in the bore. Ordinary tilting of the hot billet 10 or jolting during billet transfer has not adversely influenced the positional stability of the glass lubricant therein.

With the lubricating glass in a viscous condition, the insertion of the conical piercing point 14 into the conical opening 20 of the hot billet 10 will contact a film of glass and will continue to be in lubricating contact with the glass as the billet is forced thereover in the piercing process. We have found it advantageous during the initial installation of the lubricant in a cold billet, heating the billet with the lubricant therein and during the piercing operation to use the described sintered glass rods 22 with the fiber glass packing 24. The rods are initially formed from crushed window glass of 50 mesh size, placed in a mold and heated in a low temperature oven at 800 to 1,000F. The rod so produced will have a rough surface and will have sufficient strength for reasonable handling and placement in the billet. During heating of the billet with the glass therein, the material will adhere to the surface of the billet bore 18 and will thus provide a reservoir of lubricant which will be distributed during the piercing operation. The resultant pierced billet will have a clean smooth inner surface with a relatively low expenditure of piercing energy. Little, if any, surface conditioning of the pierced product will be necessary prior to the conversion of the pierced billet into a saleable tubular product.

What is claimed is:

l. The method of rotary piercing a hot metal workpiece of circular cross-section having a center bore extending axially through the length thereof which comprises, placing in the center opening of the workpiece a body of incombustible lubricating material having a relatively wide range of fusion temperatures below the workpiece hot working temperature, heating the workpiece material therein; rotating about a substantially horizontal axis and axially advancing the workpiece while at the predetermined hot working temperature by a skew rolling action relative to a conical piercing point with the point horizontally aligned with the center opening and the lubricating material generally symmetrically arranged in the center opening relative to the piercing point, and piercing the workpiece at such a rate the lubricating material contacting with the hot workpiece progressively fuses and forms an outer layer of fused lubricating material and a continuously thinning inner layer of relatively solid lubricating material only between the working surface of the piercing point and the portions of the workpiece contacting therewith.

2. The method of claim 1, wherein the lubricating material is glass.

3. The method of claim 2 wherein the glass comprises sintered granular window glass.

4. The method of claim 1 wherein the lubricating material comprises sintered glass rods retained in the bore of the billet by fiber glass.

Claims (4)

1. The method of rotary piercing a hot metal workpiece of circular cross-section having a center bore extending axially through the length thereof which comprises, placing in the center opening of the workpiece a body of incombustible lubricating material having a relatively wide range of fusion temperatures below the workpiece hot working temperature, heating the workpiece material therein; rotating about a substantially horizontal axis and axially advancing the workpiece while at the predetermined hot working temperature by a skew rolling action relative to a conical piercing point with the point horizontally aligned with the center opening and the lubricating material generally symmetrically arranged in the center opening relative to the piercing point, and piercing the workpiece at such a rate the lubricating material contacting with the hot workpiece progressively fuses and forms an outer layer of fused lubricating material and a continuously thinning inner layer of relatively solid lubricating material only between the working surface of the piercing point and the portions of the workpiece contacting therewith.

2. The method of claim 1, wherein the lubricating material is glass.

3. The method of claim 2 wherein the glass comprises sintered granular window glass.

4. The method of claim 1 wherein the lubricating material comprises sintered glass rods retained in the bore of the billet by fiber glass.

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